Set up Nix remote builder on this VM by following the exe.dev recipe at https://exe-staging.dev/deploy/nix-builder.md from top to bottom.

The recipe's example VM name is my-nix-builder. This VM's name is the output of `hostname`: use it wherever the recipe writes my-nix-builder. Skip the step that creates the VM; you are on it.

This recipe needs a 200GB disk, and a new VM's may be smaller. Before you install anything, run `df -h /`. If its size is under 180G, stop and ask me to grow the disk, either with this link: https://exe.dev/suggest?command=resize%20my-nix-builder%20--disk%3D200GB or, on my computer, with `ssh exe.dev resize my-nix-builder --disk=200GB`. When I say it's done, run `sudo resize2fs "$(findmnt -no SOURCE /)"`, check `df -h /` again, and carry on.

You are done when all of these are true. Check each one yourself:
- Nix with nix-daemon, `exedev` as a trusted user, building on every core, reachable over `ssh-ng://` through exe.dev's SSH
- A signing key made on the VM, its public key printed for clients
- Harmonia serving the store as a signed binary cache on port 8000, private behind the HTTPS proxy
- A nightly harmonia-gc that keeps 25% of the disk free and everything from the last 14 days, and Nix's own collection when a build runs low
- A test build on the VM whose output the cache serves with the VM's signature

Run "Set up the builder" on this VM, skipping VM creation. Everything
in "Connect a Linux machine", "Connect a Mac", "Use it from CI", and
the ssh-key and generate-api-key commands run on the owner's computers,
not here. Don't add SSH keys or tokens to the owner's account yourself.
Use the official installer from nixos.org (multi-user, --daemon); don't
install Determinate Nix here. Install Harmonia from nixpkgs as written.
Never print /etc/nix/cache-key.sec. Verify: `nix store info --store
daemon` works as exedev; `sudo -i nix config show trusted-users`
includes exedev; `curl -s localhost:8000/nix-cache-info` answers; the
test build's narinfo has a `Sig:` line with this VM's key name;
harmonia-gc.timer is enabled; if system-features has kvm, the
nix-daemon kvm.conf drop-in is in place and /dev/kvm is mode 0666
after `sudo systemctl restart nix-daemon`. Finish with this VM's CPUs, memory, and
free disk, the contents of /etc/nix/cache-key.pub, the builder's
system-features (`sudo -i nix config show system-features`), and the
owner's next steps from "Connect a Linux machine" and "Connect a Mac"
with this VM's name and public key filled in.

Finish with the URLs I should open.